1. Field of the Invention
The present invention relates to an exposure control apparatus of a camera having a plurality of exposure modes.
2. Description of Related Art
In a conventional camera having a plurality of exposure modes, a photographer can select a desired exposure by actuating an associated switch or button, etc.
In particular, in a recent camera having modes other than the exposure modes, such as a continuous shot mode, etc., the mode selection is effected by actuating a plurality of switches in combination.
However, ordinary photographers do not frequently use all of the exposure modes. Namely, only a few specific exposure modes are used. Therefore, for ordinary photographers, the need to actuate several switches in combination to select a mode is troublesome and complicated.
Furthermore, in a program exposure mode of a known camera, a shutter speed and a diaphragm value are automatically determined in a certain relationship (combination). Accordingly it is impossible for the photographer to set optional shutter speed and diaphragm values which do not satisfy the predetermined relationship while in the same mode. Furthermore, in a conventional program shifting mode, the shutter speed and the diaphragm value are always modified simultaneously while maintaining a specific relationship therebetween when the switch is actuated in the program exposure mode. Accordingly, it is impossible for the photographer to vary only the diaphragm value or shutter speed while in the program exposure mode.
Therefore, in the known camera, if the photographer wants to vary only one of the shutter speed or diaphragm value while in the program exposure mode, it is necessary for him or her to first shift the program exposure mode to another exposure mode, for example, a shutter speed priority (EE) automatic exposure mode or diaphragm priority (ES) automatic exposure mode. This, however, is troublesome. Furthermore, a desired exposure mode must be troublesomely selected from among many exposure modes in the mode shift operation.
In a manual exposure mode of a known camera, the photographer determines whether or not the exposure value is an optimum value, by observing an exposure meter provided in the field of view of a finder and manually setting the optimum shutter speed and diaphragm value to obtain an optimum exposure value. Namely, the photographer must manually set all of the exposure factors. Accordingly, freedom in the combination of the shutter speed and diaphragm value is increased. This makes it possible for the photographer to create more artistic or technical pictures.
However, it is not easy for ordinary photographers to manually adjust the optimum shutter speed and diaphragm value. In the particular, when there is a frequent change in brightness of an object to be taken, depending on the composition, it is very difficult or next to impossible for the photographer to adjust the shutter speed and the diaphragm value as quickly as the brightness changes. Furthermore it is difficult to adjust the optimum shutter speed and diaphragm value during manual zooming. The difficulty becomes more significant when it is necessary to change the mode, for example, from the manual exposure mode to the automatic exposure mode or vice versa, since the mode shift requires the operation of more than one switch.
A conventional camera has several exposure modes including a manual exposure mode in which both shutter speed and diaphragm value are manually set by a photographer, a shutter priority or diaphragm priority automatic exposure mode in which one of the two exposure factors (i.e., the shutter speed and the diaphragm value) is manually set by the photographer while the other factor is automatically adjusted to be set in accordance with the manually set diaphragm value or shutter speed, brightness of the object to be taken, sensitivity of a film to be used, etc., and a program exposure mode in which both the shutter speed and the diaphragm value are automatically set in accordance with a program diagram. The control of these exposure modes is usually performed by a microcomputer. To this end, the object brightness, the shutter speed, etc., are converted to digital APEX values before calculation.
In the prior art, the accuracy of the APEX values of the the shutter speed and the diaphragm value was generally 4/8 (1/2) step at the manual setting and 1/8 step at the automatic setting. Namely, the manual setting is less accurate than that of the automatic setting. Furthermore, the shutter speed Tv and the diaphragm value Av which can be manually set are values on an arithmetic progression having a difference of 1/2, such as 10/8, 14/8, 20/8, . . . , i.e., mixed numbers (which will be referred to as manual series values hereinafter) having an antilogarithm portion represented by 0/2 or 1/2. On the other hand, the shutter speed Tv and the diaphragm value Av which can be automatically set are values of an arithmetic progression having a difference of 1/8, such as 10/8, 11/8, 12/8, 1 3/8, . . . , i.e., mixed numbers (which will be referred to as auto series values or optimum value hereinafter) having an antilogarithm portion represented by 0/8, 1/8 . . . . Consequently, upon manual setting, it is impossible to obtain values other than the manual series values which can be set in the automatic setting, such as 1 1/8, 1 2/8, etc. In addition to the foregoing, the accuracy of the exposure value Ev and the exposure values which can be set at the manual setting are 1/2 Ev and the manual series values at the manual exposure mode and 1/8 Ev and the auto series values at the automatic exposure mode and the program exposure mode, respectively.
However, if the accuracy of the exposure factors which can be manually set and the series valises thereof are fixed, as mentioned above, it is impossible for the photographer to compose a fine detail on a picture. Conversely, if the accuracy, corresponding to the steps (intervals) between the values which can be manually set, is increased to that of the values which can be automatically set, the number of steps becomes encumbering for the photographer.